This invention relates to a method and apparatus for picking up fabric workpieces one by one from a pile of workpieces by applying vacuum and, more particularly, to detecting means to determine if the proper number of sheets have been picked up.
For the automation of sewing processes, workpiece conveyers which pick up a workpiece from a pile of workpieces and conveys it to the sewing section have been installed at many sewing factories. Such workpiece conveyers have been utilizing an apparatus which enables workpieces to be picked up one by one as shown in FIG. 4.
Referring to FIG. 4, one conventional type of apparatus for the picking up of a workpiece will be explained. Numerals 1, 2 denote vacuum pads connected to a vacuum source (not shown) and provide suction pipes 1a, 2a, respectively. Numeral 3 denotes an arm which carries the vacuum pads 1, 2. When a workpiece C1 is to be picked up from a pile 4, at first, the arm 3 descends in direction of arrow A such that the vacuum pads 1, 2 contact with a workpiece C1 and suctions the workpiece. Thereafter, the arm 3 ascends in direction of arrow B picking up the workpiece C1 from the pile 4. The arm 3 then moves in direction of C, D in succession to a photo sensor 5. The photo sensor 5 detects whether the vacuum pads 1, 2 have picked up the workpiece C1 and, if the photo sensor 5 detects the presence of workpiece C1, the arm 3 moves further in the direction of E, C in succession to a workpiece setting table (not shown). Then, by shutting off the vacuum line, the workpiece C1 separates from the vacuum pads 1, 2 and is positioned on the setting table.
In accordance with the aforementioned apparatus for picking up a workpiece, it is possible to detect whether or not workpiece is picked up but it is impossible to detect if only a single workpiece has been picked up. Generally, the workpieces are picked up one by one, but where the workpiece is very light and rarely woven, several workpieces may be picked up by suction.
To detect such mishandling, where a photo sensor is used, the sensitivity of the photo sensor is adjusted in accordance with the particular workpiece, especially with regard to color, transparency, thickness of the workpiece, etc., and so productivity is lowered. Additionally, to check by means of the photo sensor 5, the arm 3 must be moved more in direction of D, E so it takes more time and conveyer control is complicated.